Truss structure and method for construction thereof

ABSTRACT

A truss structure for use in a gravity-free environment is disclosed together with methods and apparatus for constructing the same. The structure, characterized by high stiffness and a precise self-determined geometry and having a prism-form with square right cross section, is constructed from a plurality of substantially identical triangular frame elements. The truss structure may be manually constructed from a multi-row chain of interconnected elements or from a four row network of elements. The structure may also be constructed using an automatic method wherein individual frame elements are fed from four stack support and feed units to a holding fixture having a square cross section.

This is a division of application Ser. No. 123,077, filed 11/19/87, nowU.S. Pat. No. 4,829,739, which is a division of application Ser. No.808,602, filed 12/12/85 , now U.S. Pat. No. 4,803,824.

The present invention relates in general to truss structures and toapparatus and methods for constructing and disassembling the same in agravity-free environment.

BACKGROUND OF THE INVENTION

Because of their structural efficiency, certain forms of structures arepreferred where considerations of size, weight and transportability areimportant. Among these are truss structures, which have a highstiffness-to-weight ratio and a simple, self-determined geometry. Sincethe size of these structures precludes their transport over longdistances, minimum packing volume and weight are important factors.

Among the requirements that govern the design of such structures is theuse of components that can be easily handled with a minimum amount oflabor and effort. However, structures which comply with this requirementby automatically unfolding and positioning themselves in a gravity-freeenvironment are generally not efficient and carry a weight penaltybecause of the self-deployment feature. Additionally, it is desirablethat the methods and the apparatus used for construction and disassemblybe both simple and automated to the maximum possible extent in order tominimize the requirement for human intervention. However, structureswhich are capable of automated construction at a remote site often failto achieve the necessary stiffness-to-weight ratio, stowage efficiencyand the requisite simplicity of the method and apparatus used forassembly. Also, while it would otherwise be preferred, existingstructures of the type discussed are typically incapable of constructionand disassembly at a single general location and require the equipmentin use, as well as construction performed, to move along the structureas the latter grows or diminishes in size during assembly or disassemblyrespectively.

By way of example, U.S. Pat. No. 4,259,821 to Bush discloses a trussstructure, formed from structural columns, which does not lend itself toan automated assembly method because of its complexity. U.S. Pat. No.4,337,560 to Slysh discloses a structure that lends itself to anautomated assembly technique. However, such a structure is not capableof being constructed from a single general location and it requires anassembler trolley which crawls along the structure as the structure isbuilt up during construction.

OBJECTS OF THE INVENTION

It is principal object of the present invention to provide a new andimproved space-erectable structure and construction methods thereforwhich are not subject to the aforementioned problems and disadvantages.

Another object of the present invention is to provide a truss structurehaving a high stiffness-to-weight ratio and which is constructed ofidentical repeating elements.

A further object of the present invention is to provide a trussstructure comprising discrete elements which can be efficiently stowedin a small packing volume prior to construction.

An additional object of the present invention is to provide a trussstructure which has a precise, self-determined geometry based on aplurality of identical, repeating structural elements.

Yet another object of the present invention is to provide a simplifiedassembly method for constructing a truss structure in space.

Yet a further object of the present invention is to provide apparatusand automated methods for constructing and/or disassembling a trussstructure in a gravity-free environment.

Yet an additional object of the present invention is to providephysically compact apparatus for carrying out the automated constructionof a truss structure in a gravity-free environment.

Still a further object of the present invention is to provide apparatusand methods for constructing a truss structure in a gravity freeenvironment from a single, general location.

SUMMARY OF THE INVENTION

The foregoing objects of the present invention are achieved through anew and improved prism-form truss structure and apparatus for erectingthe same. A plurality of congruent, planar, triangular frame elementsare interconnected at the element vertices to form a prism-form trussstructure having a square right cross section, which further includesdiagonal struts transverse to and spaced along the longitudinal axis ofthe truss structure.

In accordance with the present invention, the aforesaid truss structuremay be constructed manually from a chain of interconnected frameelements. The chain is folded by rotation about selected, mutuallyaligned sides of the interconnected elements until the complete trussstructure is formed. In an alternative manual construction method, anelement network comprising four rows of frame elements of equal,predetermined length is used.

The truss structure may also be constructed by using apparatus and anautomated method wherein individual frame elements are fed from fourstack support and feed units to a holding fixture having a square crosssection. As the truss structure is built around the fixture, thestructure is periodically advanced in an axial direction with respect tothe fixture to allow further truss sections to be added.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an exemplary truss structure inaccordance with the present invention;

FIG. 2 is a plan view of a frame element of the type used in theconstruction of the truss structure of FIG. 1;

FIGS. 3a and 3b illustrate a preferred truss joint;

FIGS. 4a, 4b and 4c illustrate different views of a preferred diagonalstrut for use in the truss structure;

FIG. 4d is a cross-sectional view of the strut of FIG. 4c;

FIG. 5 illustrates a variation of the structure shown in FIG. 1 havingpuckered ends;

FIG. 6 illustrates an alternative form of an A-vertex fitting;

FIG. 7 illustrates a 2-row chain of frame elements and a method ofconstructing a truss structure therefrom in accordance with the presentinvention;

FIG. 8 illustrates a 3-row chain of frame elements and a method ofconstructing a truss structure therefrom;

FIG. 9 illustrates a method of constructing a truss structure from a4-row network of frame elements;

FIG. 10 illustrates a preferred construction fixture in accordance withthe present invention;

FIG. 11 is a cross-sectional view of the construction fixture of FIG.10;

FIG. 12 illustrates the construction fixture of FIG. 10 with frameelements positioned thereon;

FIG. 13 is a plan view of a frame feed unit in accordance with thepresent invention;

FIG. 14 is a simplified sectional view showing the relationship of theconstruction fixture to the frame feed units;

FIG. 15 is a side view of a frame feed unit;

FIG. 16 is a side view of a frame feed unit during the feedingoperation;

FIG. 17 illustrates the construction fixture during the automatedconstruction operation;

FIGS. 18a, 18b and 18c are side views of a frame feed unit during thefeeding operation; and

FIGS. 19a, 19b and 19c illustrate truss shifting during the automatedconstruction of the truss structure.

DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, an exemplary truss structure 50 inaccordance with a preferred embodiment of the present invention isillustrated in FIG. 1 and comprises a plurality of substantiallyidentical triangular frame elements of the type shown in FIG. 2. Eachframe element 20 is substantially planar and consists of an A-sideA_(s), a B-side B_(s) and a C-side C_(s), located opposite an A-vertexA_(v), a B-vertex B_(v) and a C-vertex C_(v), respectively. In apreferred embodiment of the present invention, each side comprises asubstantially linear strut member. Each of the three vertices includes adifferent type of vertex fitting capable of fastening respective frameelements to one another.

In accordance with the present invention, the included angle α at vertexA_(v) is limited to a value of less than 90°. Angle α is related to thelength B of a B-side and the length C of a C-side by

    COS α=NC/4B

where N is an integer greater than 1. For values of N greater than 2,the formula defines either scalene triangular elements, or isoscelestriangular elements if B=C, from which the truss structure of thepresent invention may be constructed. In accordance with a preferredembodiment of the invention, N=2 to define isosceles triangular elementswherein sides A_(s) and B_(s) are substantially equal in length andwherein length C=2B/√3. For the sake of illustration only and without solimiting the invention, the truss structure of FIG. 1 is illustrated asbeing constructed from ten of the aforesaid preferred elements.

A joint 21 of truss structure 50 (FIG. 1), where three frame elements ofthe truss are joined, is shown in FIG. 3a broken away from thestructure. Vertex C_(v) is shaded for the sake of illustration only, inorder to distinguish it from vertices A_(v) and B_(v) to which it isjoined. FIG. 3b shows an exploded view of joint 21 wherein vertex A_(v)comprises a fitting 22 which includes a socket 24. Vertex B_(v)comprises a fitting 26, which includes a socket 28 and a fastening pin30 shown fixed in the socket. Vertex C_(v) comprises a fitting 32 whichincludes a tab 34 containing a through hole 36. Pin 30 need not be fixedin vertex B_(v) and in fact may be fixed in either vertex A_(v) or C_(v)depending on the method of construction used. As can be seen in FIG. 2,the axis of through hole 36 is parallel to that of side C_(s). Therespective axes of sockets 24 and 28 are coincident and aligned with theaxis of side C_(s).

Each hinged joint of the truss comprises the A-, B- and C-vertices ofthree different frame elements which are fastened together. As seen inFIG. 3b, irrespective of the fitting in which the fastening pin isinitially fixed, the pin aligns with and engages through hole 36 invertex fitting 32, socket 24 in vertex fitting 22 and socket 28 invertex fitting 26.

As seen in FIG. 3b, beveled surfaces 86, positioned on opposite sides ofeach fitting, are respectively inclined at an angle of approximately 45°with respect to the frame element plane. Surfaces 86 are only visible onone side of each fitting 22 and 26 in FIG. 3b. Surfaces 86 are adaptedto limit the relative angular position between the planes of frameelements fastened together, such that the angle between the planes ofadjacent joined elements cannot be less than 90°. Thus, in FIG. 3awherein elements 75, 77 and 79 form joint 21, the relative angularposition between the plane of element 75 which carries the A-vertexfitting and the plane of element 77 which carries the C-vertex fittingis limited to a minimum of 90°. At the 90° relative angular positionbetween elements 75 and 77, portions of the respective bevel surfaces 86of the elements contact each other. The same limitation applies to therelative angular position between the respective planes of element 77and element 79 which carries the B-vertex fitting.

Vertex fittings 22, 26 and 32 respectively include lock screw holes 38,40 and 42. Lock screw holes 38 and 40 in fittings 22 and 26 respectivelycommunicate between the surface and socket of the respective fitting.Lock screw hole 42 communicates between the surface of vertex fitting 32and through hole 36. Each lock screw hole is adapted to receive a lockscrew (not shown) which, when tightened, is effective to retain afastening pin inserted into the respective fitting.

Referring again to FIG. 1, truss structure 50 is seen to comprise aprism-like structure, having four longitudinal edges 52, 54, 56 and 58parallel to a central axis 60 and having a right cross section in theform of a square. Each longitudinal edge 52, 54, 56 and 58 respectively,consists substantially only of the C-sides of the respective frameelements. A plurality of diagonal struts 62 interconnect points alongdiagonally opposite longitudinal edges, each such point being located atthe joint of a plurality of vertex fittings. In the embodiment shown inFIG. 1, each diagonal strut 62 is substantially linear and intersectsaxis 60 substantially perpendicularly thereto. While the use of diagonalstruts provides necessary rigidity to the truss structure, it may bepossible, by the proper choice of frame element dimensions, to dispensewith them.

The details of a preferred diagonal strut are illustrated in FIG. 4.Referring to FIG. 4a, strut 62 is seen to include a pair of endconnectors 64, affixed at opposite ends in alignment with a strut strutaxis 65. FIG. 4b shows the details of end connector 64, which is seen toinclude a cylindrical head portion 66 having an end face 68 and a hole70. The hole is coaxial with the strut and is adapted to hold a strutpin. In the preferred embodiment of the present invention, the strut pintakes the form of a threaded stud 72. Referring to FIGS. 4c and 4d, stud72 is seen to consist of two portions, a threaded portion 74 and asmooth portion 76 having a larger diameter than the threaded portion andincluding two flat keyways 78 located diametrically opposite each other.The connector further includes a lock screw 80 and a key 82 positioneddiametrically opposite each other and respectively adapted to fit intokeyways 78. With lock screw 80 loosened, stud 72 is free to slideaxially within hole 70, but is constrained from rotation about axis 65by the key. The threading of studs 72 at opposite ends of strut 62 is inmutually opposite directions, each stud being adapted to engage asuitably threaded hole 84 in a C-vertex tab 34, as best shown in FIG.3b.

The free vertex points 85 and 87 at the left-hand terminating end ofstructure 50, as viewed in FIG. 1, are seen to be joined together by anend strut 88. Vertex point 87 is further connected to point 89 of thestructure by an end strut 90. The free vertex points 91 and 93 at theright-hand terminating end of the truss structure are joined together byan end strut 92. Point 91 is further connected to point 95 of thestructure by an end strut 94. Each end strut 88 and 90 is preferablyidentical to the strut used for side B_(s) of a frame element, hereafterreferred to as a B-end strut, and carries vertex fittings 22 and 32 onits respective ends. Each end strut 92 and 94 is preferably identical tothe strut used for side A_(s) of a frame element, hereafter referred toas an A-end strut, and carries vertex fittings 26 and 32.

A truss structure constructed from the preferred elements alwaysincludes two B-end struts on one terminating end and two A-end struts onthe opposite end. As shown in FIG. 1, each end of the truss shown thereis "planar", the plane at the left hand end being defined by vertexpoints 83, 85, 87 and 89 and at the right hand end by vertex points 91,93, 95 and 99. However, the ends of such a structure, once the endstruts are in place, need not be "planar". Either or both terminatingends of such a structure may be "puckered", as shown in an alternativeembodiment 96 illustrated in FIG. 5. The free vertex points 101 and 103at the left-hand terminating end of structure 96 are respectively joinedto the structure by B-end struts 98 and 100. The free vertex points 105and 107 at the right-hand end of the structure are respectively joinedto the structure by A-end struts 102 and 104.

The method of constructing the aforesaid truss structure in agravity-free environment from substantially identical triangular frameelements lends itself to a number of variations. In one embodiment, theframe elements are initially arranged as a chain comprising at least tworows of frame elements. For a truss structure comprising elementsdefined by the above-described equation, COS α=NC/4B, the value of Ncorresponds to the number of rows in the chain.

In one variation of this method, a 2 row chain comprising the preferredelements is used, i.e. where N=2 and C=2B/√3 in the above-describedequation. Referring to FIG. 7, such a chain 122 comprises elementsarranged in two rows of equal length, respectively designated row 1 androw 2. The sides of the respective elements are designated A_(s), B_(s)and C_(s), as in FIGS. 1 and 2.

In each row of elements, the A-vertex of each element is hingedly joinedto the C-vertex of the adjacent element. Except for certain elements atthe ends of a chain, the B-vertex of each element forms a hinged jointwith the proximate A- and C-vertices of elements in the adjacent row.This applies to each but the Nth row of the chain, i.e. row 2 of chain122. At each location where at least two frame elements are joined,fastening pin 30 is present and is rigidly held in the A- or B-vertexfittings, or in both where both vertex fittings are present, bytightening the lock screws located therein. The lock screw in thethrough hole of the C-vertex fitting at each such location is leftuntightened. This arrangement permits freedom of rotation about thethrough hole axis in the element carrying the C-vertex, with respect tothe other element or elements carrying fittings joined thereto.

The configuration of the A-vertex fitting of selected elements in thechain formed as part of this construction method differs from that shownin FIG. 3. Referring to FIG. 6, the A-vertex fitting in these selectedelements includes a retractable fastening pin 116 which has a slot 118,all within vertex fitting 22. Fitting 22 further includes a slot 120which extends into element side C_(s). By inserting a tool, such as theblade of a screwdriver, into slot 118 and moving it along the length ofslot 120, pin 116 may be extended out of, or retracted into, fitting 22.

With respect to the chain of elements illustrated in FIG. 7, eachA-vertex of a row 1 element is fitted with the above-describedretractable fastening pin. Referring again to FIG. 6, in row 1 of thechain, pin 116 is extended into through hole 36 of C-vertex fitting 32of the adjacent element, and the lock screw (not shown) in the A-vertexfitting is tightened.

Referring again to FIG. 7, the method proceeds with a first element 113in row 1 of the chain and folding in succession along parallel foldinglines 112-1, 112-2, 112-3, etc. Each such folding line comprises eithera single C-side of a frame element, or two mutually aligned C-sides ofdifferent frame elements. Each fold is made by rotating the element orelements being folded in a predetermined rotational sense 114 throughsubstantially 90°. The contact established between bevel surfaces 86limits each rotation to 90°. At the completion of each 90° rotation, thelock screws in the C-vertex fittings which lie along fold line 112 aretightened against further rotation. Upon completing the third rotationand upon each rotation thereafter, the C-vertex fitting of the firstelement in row 1 and, subsequently, the hingedly joined A- andC-vertices of the row 1 elements are brought into confrontation with thefree B-vertices of the row 2 elements.

The triad of elements carrying the vertex fittings at these confrontingvertices are then joined to form hinged joints. Joining is achieved byloosening the lock screw in the A-vertex fitting of the appropriateelement in row 1, aligning the row 2 B-vertex socket with pin 116,extending the pin into the socket of the row 2 element B-vertex fittingand tightening the lock screws in the A-, B- and C-vertex fittings beingjoined.

In one variation of the method of constructing a truss structure from achain of elements, B-end struts 124 and 125 are installed following thethird rotation. Their respective positions, as well as those of A-endstruts 126 and 127, are shown for the chain in FIG. 7 for illustrativepurposes. Thus, the end of strut 125, which carries an A-vertex fitting,is joined to the B-vertex fitting of the third element in row 2 and tothe C-vertex of the first element in row 1, to form a hinged jointtherewith. The end of strut 124, which carries an A-vertex fitting, isjoined to the B-vertex fitting of the second element in row 2 and to theend of strut 125 which carries a C-vertex fitting, to form a hingedjoint therewith. The end of strut 124 carrying a C-vertex fitting ishingedly joined to the B-vertex fitting of the first element in row 2.

A-end struts 126 and 127 are installed after folding of the chain hasbeen completed. The end of strut 126 carrying a C-vertex fitting ishingedly joined to the A-vertex fitting of the last element in row 1.The end of strut 127 carrying a C-vertex fitting is joined to theA-vertex fitting of the last element in row 2 and to the end of strut126 carrying a B-vertex fitting, to form a hinged joint therewith. Theend of strut 127 carrying a B-vertex fitting is joined to the hingedlyjoined A- and C-vertex fittings belonging to the third from last elementand the second from last element respectively in row 1, to form a hingedjoint therewith.

After completing the above-described steps, the diagonal struts may beinstalled in the truss structure. Referring again to FIG. 4, eachdiagonal strut may be installed by positioning it between theconfronting C-vertex fittings on diagonally opposite longitudinal edgesof the structure. The threaded portion 74 of each stud 72 at each strutend engages hole 84 in the proximate C-vertex tab. With lock screw 80loosened, the stud may be slid into hole 70 so that the threaded portionextends beyond end face 68 by a small distance. The length of strut 62is selected to enable the extended portions of the studs at oppositestrut ends to engage holes 84. Thereafter, the strut is tightened inposition by rotating it about axis 65. This rotation and the fact thatthe studs are threaded in mutually opposite directions, causes each stud72 at opposite ends of strut 62 to be drawn out of its hole 70. Eachstud is free to move axially while lock screw 80 remains loosened.Tightening of the stud is complete when end face 68 at each end of thestrut contacts the proximate C-vertex tab. Lock screw 80 at each strutend is now tightened to prevent further axial movement of the stud.

FIG. 8 schematically illustrates a 3-row chain 110 of elements, eachelement being defined by the aforesaid equation, wherein N=3 and B=C.The respective rows of the chain are designated row 1, row 2 and row 3.The sides of the respective elements are designated A_(s), B_(s) andC_(s), as in FIGS. 1 and 2. To construct a truss structure from a chaincomprising three or more rows, the steps of folding, locking and joiningproceed essentially as described with respect to the 2-row chain shownin FIG. 7. The 3-row chain in FIG. 8 shows folding lines 112 and furtherindicates the rotational sense 114 for illustrative purposes. Asdiscussed above, however, the configuration of the end struts willdiffer for structures where N>2.

The present invention is not limited to the chain method of constructiondescribed in connection with FIGS. 7 and 8. In accordance with a furtherembodiment of the construction method, the structure herein may be builtin a gravity-free environment from frame elements which are initiallyarranged as a network consisting of four rows. In one embodiment of thismethod, the network comprises the preferred elements for which N=2 andand C=2B/√3 in the above-described equation. Referring to FIG. 9, anetwork 128 includes four rows of elements, designated rows 1 to 4. Ineach row, the A-vertex of each element is hingedly joined to theB-vertex of the adjacent element. With the exception of the elements inrow 1, the C-vertex of each element in the network forms a hinged jointwith the proximate A- and B-vertices of elements in the adjacent row. Inone form of the embodiment under discussion, two B-end struts 132 and133 and two A-end struts 134 and 135 are added to the initial network offrame elements, as shown in the drawing.

The end of B-end strut 132, which carries an A-vertex fitting, is joinedto the B-vertex of the first element in row 4, as indicated at 139. Theend of strut 132 carrying a C-vertex fitting is joined to the B-vertexof the first element in row 3 at point 141. The end of B-end strut 133,which carries an A-vertex fitting, forms a hinged joint with theC-vertex of the first element in row 3 and the B-vertex of the firstelement in row 2 at point 143. The end of strut 133, which carries aC-vertex fitting, is joined to the B-vertex of the first element in row1 at point 145.

The end of A-end strut 134, which carries a B-vertex fitting, is joinedto the A-vertex of the last element in row 4 at point 147. Each A-vertexof an element in row 4 is preferably fitted with a retractable fasteningpin previously described and illustrated in FIG. 6. The pin extends intothe B-vertex of the adjacent element or end strut. The end of strut 134carrying a C-vertex fitting is joined to the A-vertex of the lastelement in row 3 at point 149. The end of A-end strut 135, which carriesa B-vertex fitting, forms a hinged joint with the C-vertex of the lastelement in row 3 and the A-vertex of the last element in row 2 at point151. The end of strut 135, which carries a C-vertex fitting, is joinedto the A-vertex fitting of the last element in row 1 at point 153.

At each location where frame elements are joined, fastening pin 30 isrigidly held in the A- and B-vertex fittings upon tightening the lockscrews in those fittings. However, the lock screw in the through hole ofthe C-vertex fitting at each such location is left untightened. Thisresults in freedom of rotation about the through hole axis for theelement which carries the C-vertex fitting. Such rotation may occurrelative to the other two elements which carry, respectively the A- andB-vertex fittings joined to the C-vertex fitting. As a consequence ofthis freedom of rotation, the aligned C-sides of the elements of rows 3,2 and 1 respectively, constitute three folding lines 136, 138 and 140.

The construction of a truss from the network shown in FIG. 9 commencesby rotating the elements of row 4 in unison about folding line 136 in apredetermined rotational sense 142 through substantially 90°. Therotation proceeds until contact is established between bevel surfaces 86of the elements of row 3 at an angle of rotation of about 90°. At thecompletion of the rotation the lock screws in the C-vertex fittings ofthe elements and end struts in row 4 are tightened against furtherrotation. Next, with row 4 locked at a 90° angle relative to row 3, theelements of row 3 are rotated in unison about folding line 138 in therotational sense shown by arrow 142. This rotation is again limited to90°, by virtue of contact between the bevel surfaces 86 of the elementsof rows 3 and 2. Upon completion of the last-described 90° rotation, thelock screws in the C-vertex fittings of the elements in row 3 aretightened against further rotation. Finally, the elements in row 1 areindividually rotated through substantially 90° about folding line 140,in a rotational sense 144 opposite to the direction 142. This results ineach pair of hingedly joined A- and B-vertex fittings in row 4 beingbrought into confrontation with a C-vertex fitting of a row 1 element.The confronting elements of each triad of elements are then joined byloosening the lock screws in the A- and B-vertex fittings of eachelement of row 4, retracting each pin 116 into its A-vertex fitting,aligning the through hole axis of each C-vertex fitting of row 1 withthe axis of the pin, extending the pin first through the C- and theninto the B-vertex fitting of the elements being joined and tighteningthe lock screws in all three vertex fittings. Upon completion of theabove-described steps, diagonal struts 62 are installed in the mannerpreviously discussed to complete the truss structure.

A preferred method of constructing a truss structure in accordance withthe present invention uses automated apparatus to position therespective frame elements in a gravity-free environment and to fastenthem in place. FIG. 10 shows a construction fixture 146 which has anelongate prism shape and a square cross section. Four longitudinal edges148, 150, 152 and 154 are parallel to a longitudinal axis 156. Theplanes defined between the longitudinal fixture edge constitute solidfaces in the preferred embodiment of the invention, as shown at 158,160, 162 and 164. However, where the longitudinal edges are adapted toprovide adequate support for frame elements deposited upon fixture 146during construction of the truss structure, the solid fixture faces canbe be dispensed with.

Fixture 146 is coaxially mounted on a rigid beam 166 and is axiallymovable therealong. As best shown in FIG. 11, beam 166 includes fourradial web members 168, each terminating in a widened track portion 170.Web members 168 are angled at 90° relative to each other such that trackportions 170 extend to the four corner regions 172, 174, 176 and 178 offixture 146. The intersection of members 168 is centered on axis 156 offixture 146. A plate 180 bridges each corner region and extendssubstantially the entire length of fixture 146. In the preferredembodiment, each plate 180 may be fitted with a rack engaged by a piniongear 182 mounted on each track portion 170 of beam 166. At least onepinion gear may be powered in order to drive fixture 146 on commandrelative to beam 166.

During construction, one end of beam 166 is affixed to a location on areference surface 184, such as the surface of a vehicle in gravity-freespace. A pair of retractable fixture pins is disposed along each of thefour longitudinal fixture edges 148, 150, 152 and 154. Pin pairs 186,188; 190, 192; and 194, 196 are visible in FIG. 10. When extended, eachpair of fixture pins acts to hold two vertices of a frame element, thethird vertex being supported by being joined to the mating vertex of anadjacent frame element. As a result, the frame element is securely heldon fixture 146 during construction. Each fixture pin preferably has anaxis which lies along the bisector of the angle formed by the fixtureplanes which intersect in the edge where the pin is located. Forexample, each of pins 186 and 188 is capable of selectively retractingalong its axis which forms a 45° angle with each of fixture planes 158and 164. The mechanisms (not shown) for extending and retracting therespective fixture pins are positioned in corner regions 172, 174, 176and 178.

FIG. 12 shows fixture 146 with two frame elements, designated I and IIIrespectively, positioned on fixture planes 158 and 160. Element I hassides designated 1A, 1B and 1C and vertices designated A_(v1), B_(v1)and C_(v1). Element III has sides designated 3A, 3B and 3C and verticesdesignated A_(v3), B_(v3) and C_(v3). Each fixture pin, when extended,engages a mating fixture pin hole 198, shown in FIG. 3, located at thevertex of a suitably positioned frame element. For example, in thearrangement in FIG. 12 fixture pin 190 extends from edge 150 of fixture146 to engage the mating fixture pin hole in vertex B_(v1) of frameelement I. Fixture pin 192 likewise extends from fixture edge 150 toengage a mating fixture pin hole in vertex A_(v1) of element I, thelatter thus being held in position on fixture 146 by fixture pins 190and 192. Similarly, fixture pins 194 and 196 extend from fixture edge152 to respectively engage mating fixture pin holes in vertices B_(v3)and A_(v3) of element III, which is thereby held on fixture 146.

A retractable torquing device extends from each longitudinal fixtureedge. Torquing devices 199, 200 and 202 are visible in FIGS. 10 and 12,extending from fixture edges 148, 150 and 152 respectively. Eachtorquing device is adapted, when extended as shown, to engage thealigned lock screw at an A-vertex fitting, specifically the lock screwlocated in hole 38 of vertex fitting 22 in FIG. 3. This alignment occurswhen a frame element is held in position on fixture 146 by theappropriate fixture pins. Each torquing device is capable of tighteningor loosening the lock screw aligned therewith while constructing ordisassembling, respectively, the truss structure. The mechanisms (notshown) for actuating the respective torquing devices are positioned incorner regions 172, 174, 176 and 178.

FIG. 13 is a plan view of a frame feed unit 204 with frame elements 20stacked thereon. As shown in FIG. 14, first, second, third and fourthframe feed units, designated 206, 208, 210, and 212 respectively, arespaced 90° from one another around longitudinal axis 156 of fixture 146.Feed units 206 and 208 are positioned diametrically across from eachother, as are feed units 210 and 212. Further, feed units 206 and 208are equidistantly spaced from reference surface 184 and axially spacedfrom feed units 210 and 212. The latter feed units are likewiseequidistantly spaced from the reference surface and are axiallypositioned closer to the reference surface than feed units 206 and 208by a distance substantially equal to one-half the length of an elementside C_(s).

Referring again to FIG. 13 and also to FIG. 15, feed unit 204 comprisesthree substantially identical telescoping guide post 214 perpendicularlymounted to a base plate 216. The guide posts are located on the baseplate in a pattern which conforms to the triangular configuration ofelements 20. Each guide post 214 contains a telescoping shaft 218 andincludes means, not shown, for driving shaft 218 to a desired position.Thus, in effect the free end of each guide post (actually the free endof shaft 218) can be extended outward. Guide posts 214 have a lengthchosen to support a predetermined number of frame elements in a stack220. The size of the stack carried by the guide posts of the respectiveframe feed units 204 determines the number of frame elements that can beadded to the truss structure to be constructed before each feed unitmust be replenished with additional frame elements. The free end of eachshaft 218 is fitted with a selectively retractable end pin 222. Uponextension, each end pin 222 is adapted to engage a mating vertex hole224 located on the inside of the vertex fittings at each vertex A.sub.v, B_(v) and C_(v).

Each feed unit 204 further includes three substantially identical beltunits 226, each positioned within stack 220 and mounted on base plate216 adjacent one guide post 214. As best shown in FIG. 15, each beltunit 226 includes a belt 228 mounted on a pair of pulleys 230, such thatbelt 228 is perpendicular to the base plate. In one form of feed unit,belt units 226 are free-wheeling and no forced driving means areprovided. Each belt includes contours 232 which mate with frame elements20 in stack 220.

Referring now to FIG. 16, the selected frame element 20A on top of stack220 is held by pins 222. To move frame element 20A away from base plate216, shafts 218 extend out of guide posts 214 and all three belts 228rotate by the span of one contour 232. Belt rotation, produced bycontact between moving frame element 20A and the proximate contour 232of each belt 228, causes the remaining elements in the stack, by theircontact with the belt contours, to move in unison up toward the freeends of guide posts 214. Conversely, when an element is added to the topof the stack during disassembly of the truss structure, the belts willrotate in the opposite direction and cause the frame elements in thestack to move down on the guide posts toward base plate 216. It will beunderstood by those skilled in the art, that the terms "up" and "down"are used in a relative sense herein for purposes of explanation and notin their absolute sense.

As seen in FIG. 14, each feed unit 204 is disposed in fixed relationshipto reference surface 184 opposite one plane or face of fixture 146. Thestacked elements are preferably positioned parallel to the confrontingfixture plane.

In the automated construction method, the frame elements defined by theabove-described equation, COS α=NC/4B, preferably have dimensions asdetermined by N=2 and C=2B/√3. Additionally, fixture pin 30 is initiallyfixed in B-vertex fitting 26 of each element, as illustrated in FIG. 3.Using the aforesaid frame elements, the truss structure herein may bestarted with a variety of different end configurations. For example,referring to FIG. 5, a puckered end 97, using B-end struts 98 and 100,may initiate the truss structure.

By way of example, the assembly of a truss structure having theaforesaid puckered end configuration will be explained, using theabove-described automated construction apparatus. Four frame elementsare initially fed in sequence from feed units 206, 208, 210 and 212 tothe fixture faces confronting each feed unit. As shown in FIG. 17, theseelements are designated I, II, III and IV. Each feed unit feeds elementsto its respective confronting fixture face in identical manner.

FIG. 18 illustrates in side view the operation of feed unit 206 in theprocess of feeding element I to fixture face 158. Referring to FIG. 18a,base plate 216 of feed unit 206 moves from an initial position through adistance F in a backward axial direction toward reference surface 184.Distance F is greater than the length of the portion of fixture pin 30which extends from fitting 26. Shafts 218 on the feed unit, havingelements 20 stacked thereon, are positioned to align end pins 222 withthe vertices of element I on top of the stack. To "select" frame elementI, end pins 222 are extended to engage mating holes 224 as well as thevertex fittings of element I. The simultaneous engagement of holes 224by end pins 222 at vertices A_(v1), B_(v1) and C_(v1) of element I onstack 220 is effective to "select" element I, i.e. to hold it.

Next, referring to FIG. 18b, shafts 218 are extended out of guide posts214 to thereby move element I in a direction away from base plate 216and toward the confronting fixture face. Element I is thus placed inconstruction position in confronting fixture face 158 with side 1Caligned with fixture edge 148 (FIG. 17). Thereafter, as shown in FIG.18c, base plate 216 of feed unit 206 moves from its current positionthrough distance F in a forward axial direction, i.e. away fromreference surface 184. The resulting position of element I is as shownin FIG. 17. Following the feeding of element I to the fixture, fixturepins 190 and 192 are extended to engage and hold element I on thefixture. Shafts 218 of feed unit 206 remain extended engaging theelement.

In the manner just described, second feed unit 208 feeds a frame elementII to fixture face 162. Element II has sides designated 2A, 2B and 2Cand vertices designated A_(v2), B_(v2), and C_(v2). Fixture pins (notshown) are extended to engage and hold element II on the fixture. Shafts218 of feed unit 208 remain extended to engage element II.

Thereafter, the third feed unit 210 feeds element III, having side andvertex designations as previously described, to fixture face 160. Theforward axial movement of feed unit 210 is effective to insert thefastening pin fixed in vertex B_(v3) of element III into the throughhole in vertex C_(v2) of element II. Fixture pins 194 and 196 areextended to engage and hold element III on the fixture. Shafts 218 offeed unit 210 remain extended to engage the element.

Next, fourth feed unit 212 feeds a frame element IV to fixture face 164.Element IV has sides designated 4A, 4B and 4C and vertices A_(v4),B_(v4) and C_(v4). The forward axial movement of feed unit 212 iseffective to insert the fastening pin in vertex B_(v4) of element IV andinto the through hole in vertex C_(v1) of element I. Fixture pins 186and 188 are extended to engage and hold element IV on the fixture.Shafts 218 of feed unit 212 remain extended to engage element IV.

B-end struts 98 and 100 are manually installed next. As shown in FIG. 5,end strut 98 extends between the free vertex consisting of vertex B_(v1)of element I and the joined C_(v2) and B_(v3) vertices of elements IIand III respectively. Fastening pin 30, which is fixed in vertex B_(v3)and already extends through the through hole in vertex C_(v2) of elementII, now additionally engages socket 24 of the A-vertex fitting attachedto one end of strut 98. With respect to the other end of strut 98,fastening pin 30, which is fixed in vertex B_(v1) of element I, isinserted through the through hole of the C-vertex fitting attached tothe other end of the strut. The lock screws in the fittings at therespective ends of strut 98 are then tightened.

End strut 100 extends between the free vertex consisting of vertexB_(v2) of element II and the joined vertices C_(v1) and B_(v4) ofelements I and IV respectively. Fastening pin 30, which is fixed invertex B_(v4) and which is already inserted through the through hole invertex C_(v1), now engages socket 24 of the A-vertex fitting attached toone end of strut 100. With respect to the other end of strut 100,fastening pin 30, fixed in vertex B_(v2), is inserted through thethrough hole of the C-vertex fitting attached to the other end of thestrut.

Following the installation of the fourth element, the fixture, which nowholds elements I, II, III and IV thereon, is axially moved in a forwarddirection, i.e. away from surface 184, to enable the feeding ofadditional elements from the feed units. Prior to the aforesaid axialfixture movement, shafts 218 of feed units 206, 208, 210 and 212 aredisengaged from elements I, II, III and IV respectively, by retractingend pins 222 from the respective elements and then withdrawing theshafts from those elements. Fixture 146 is then moved in the forwardaxial direction through a distance T, where T is substantially equal toC_(s), i.e. to the length of a C-side.

Next, each feed unit 206, 208, 210 and 212, in sequence, feeds oneelement to its respective confronting fixture face, thus bringing toeight the total number of elements fed to the fixture. The forward axialmovement of each feed unit is effective to join a triad of elements.This is accomplished by first inserting the fastening pin fixed in theB-vertex of the element being fed into the C-vertex through hole of apreviously fed element positioned on the adjacent fixture face nearestthe C-side of the element currently being fed, and then into theA-vertex socket of the element previously fed by the current feed unit.Following the forward axial movement of each feed unit, the torquingdevice aligned with the lock screw in the A-vertex fitting of theelement previously fed by the current feed unit is extended to engageand tighten the aligned lock screw. Shafts 218 of each feed unit remainextended to engage the last fed element. Thus, a total of eight elementsare joined to each other.

Following the installation of the element resulting from the secondfeeding operation by the fourth feed unit (herein the eighth elementinstalled), and following the installation of each fourth elementthereafter, the completed portion of the truss structure is shifted in aforward axial direction along fixture 146 in order to expose a furtherportion of the fixture and to permit the addition of further elements tothe truss. The respective axial positions of the fixture and of theportion of the structure built up to that point in time are showndiagrammatically in FIG. 19 for this operation. FIG. 19 provides a sideview of fixture face 158 and shows only the frame elements I and V.While the shifting operation is described below primarily with referenceto fixture face 158 and the aforesaid elements I and V, it will beunderstood that, at the indicated stage of construction of the trussstructure, a pair of elements is mounted on each of the other threefixture faces and that operations similar to those performed withrespect to elements I and V are simultaneously performed with respect tothe elements not shown.

Following the installation of the second element fed from fourth feedunit 212, the two elements designated I and V are positioned on face 158opposite first feed unit 206, as shown in FIG. 19a. Element I is held onface 158 by fixture pins 190 and 192 (FIG. 18). Element V is held on endpins 222 of the guide post shafts of feed unit 206. Additionally,element V is held in place by virtue of being joined to adjacentelements at its respective vertices.

Fixture pins 190 and 192 are retracted to release the hold of fixture146 on element I. While the structure is held on the end pins of theguide post shafts of the four feed units, fixture 146 is moved axiallybackward along axis 156 toward reference surface 184 by the previouslydefined distance T. The new fixture position is shown in FIG. 19b.Fixture pins 190 and 192 are now extended to engage element V. The endpins on the guide post shafts of the first feed unit are retracted fromelement V and the shafts are withdrawn from the element. As a result,the structure, comprising elements I and V plus six elements not shown,is held solely by fixture 146.

Next, as shown in FIG. 19c, fixture 146 is moved axially forward throughdistance T, carrying with it the truss structure. Upon completing thismovement, the fixture is in position to receive for assembly anadditional element on fixture face 158 and three additional elements onthe three invisible fixture faces. The automatic procedure describedabove is now repeated to construct a further section of the trussstructure by the addition of four more frame elements.

The foregoing steps are repeated until the stacks of elements have beenexhausted and no further replenishment of the stacks is required, suchthat a truss structure of the desired length has been constructed.Diagonal struts 62 are installed next in the manner previouslydescribed. Further, two A-end struts are manually connected to the freevertex points on the right hand end of the truss structure, as seen inFIG. 5, where construction is complete.

As previously discussed, a number of different end configurations of thestructure are possible and the connections of the end struts to the freevertex points and the structure will depend on the specific endconfiguration selected.

In general, by withholding delivery of an element from feed units 206 or208 in the initial sequence of elements, a structure with a planar endwill result, rather than the puckered end shown in FIG. 5. Additionally,by withholding delivery of three elements by feed units 206, 208 and212, or by withholding three elements from feed units 206, 208 and 210in the initial sequence of elements, a planar structure end will alsoresult. For example, if prior to the initial forward axial movement offixture 146 through distance T one element is fed from feed unit 210 andif no elements are fed from feed units 206, 208 and 212, the resultantleft-hand end configuration of the structure will be planar with theorientation shown in FIG. 1. The planar end is always parallelogramshaped and forms an oblique angle with the axis of the structure.

In similar manner, the configuration of the right hand end of the trussstructure may be varied. Thus, if the last four elements of thestructure are delivered by feed units in sequence 206, 208, 210 and 212(FIG. 14), the right-hand end of the structure will be puckered and willappear as in FIG. 5. In such a case, two A-end struts 102 and 104 willbe installed with each end strut interconnecting a free vertex to ajunction of a pair of element vertices on structure 96. As a furtherexample, if the last four elements of the structure are delivered byfeed units in the sequence 208, 210, 212 and 206, the right-hand end ofthe structure will be planar and will appear as in FIG. 1. As seen inFIG. 1, one A-end strut 92 is installed to interconnect the freevertices, while an additional A-end strut 94 is installed tointerconnect one free vertex with the structure.

Since the left and right hand end configurations may be variedindependently of each other, a completed truss structure may possess anydesired combination of planar or puckered end configurations. Forexample, both ends may be planar and oriented to be parallel to eachother.

In order to disassemble the truss structure using the above-describedautomated apparatus, in one variation, all the diagonal struts mustfirst be manually removed. Then, the order of the steps of theconstruction method described above is substantially reversed and eachtorquing device is operated to loosen rather than to tighten the lockscrew in each A-vertex. The guide posts extend and retract in order tocarry individual frame elements from the truss structure back to thefeed units where the frame elements are accumulated in four stacks. Withrespect to the diagonal struts, in another variation, instead ofremoving all of them prior to the structure disassembly, each strut maybe manually removed as its position approaches the construction fixtureduring the disassembly. In the latter case, the structural integrity ofthe truss structure is maintained during disassembly, which isespecially desirable if the truss structure is long or includes apayload mounted on its free end.

As disclosed herein, the automated construction method illustrated anddescribed utilizes feed units with frame elements stacked thereon.However, the stacks and the associated belt units may be dispensed with,if desired. For example, each feed unit may be fitted with relativelyshort guide posts and be positioned relative to the construction fixturesubstantially as in the preferred embodiment of the invention. The frameelements may be supplied individually to each feed unit, by transportingthem in a direction parallel to the axis of fixture 146. Thus, eachframe element may be introduced into the space between the feed unit andthe confronting fixture face. Each frame element in such a method isoriented so as to be substantially parallel to the fixture face whichconfronts the particular feed unit. The guide post shafts can then beextended to engage the newly introduced frame element to position it onthe confronting fixture face. The balance of the procedure then followsthe method described above with respect to the automated construction.One technique for individually supplying the frame elements from aremote point, rather than from a stack, may use a pallet or the likewhich moves on tracks. The tracks may be mounted on an extended portionof fixture 146 adjacent reference surface 184.

A major advantage of individually supplying the frame elements is todecouple the size of the completed truss structure from the stackcapacity of the feed units. A further advantage is to reduce the volumeof space required for the construction apparatus, since stacks are nolonger required.

While in the automated method disclosed herein the B-end struts aremanually installed, the invention is not so limited. Initially, eachB-end strut may be positioned on top of the element stack on the feedunit confronting the prospective installed location of the strut. Eachof the B-end struts so positioned are held in place on the stack by thestrut's engagement with end pins 222 of feed unit guide posts 214. Then,in order to install the strut, shafts 218 are extended out of guideposts 214 to deliver the end strut to the confronting fixture face.

The automated construction method illustrated and disclosed hereinincludes the installation of end struts on the end of the trussstructure when construction is completed. However, under certainoperating conditions in gravity-free space, the truss structure mayremain mounted on fixture 146 following the completion of assembly,being held thereon by the fixture pins. In the latter case the fixture,which itself remains attached to reference surface 184 through beam 166,supplies the requisite structural integrity at the end of the trussstructure. Such an arrangement may be used, for example, where the trussstructure is utilized to deploy a payload such as sensors or solarcollectors, which are mounted on the end of the structure whereconstruction was initiated.

In the case where a payload is to be mounted on the end of the structurewhere construction is initiated, an initial group of frame elements maybe preassembled to form an initial end of the structure and the payloadjoined thereto. Then the preassembled elements and payload are mountedon the construction fixture and upon commencement of the automatedconstruction, the elements initially fed to the fixture are joined tothe preassembled elements.

An automated construction method has been disclosed wherein the feedingof an element to the construction fixture includes an axial movement,through a distance F, of the feed unit feeding the element. However, itis the relative axial movement through distance F between the fixtureand the feed unit that is necessary to accomplish the element feedingoperation. Thus, the feeding of the element may be accomplished withequal effect by axially moving the fixture through the distance F whilethe appropriate feed unit remains stationary.

In the automated construction method disclosed herein, diagonal struts62 are installed following construction of a truss structure of thedesired length. Alternatively, this operation can be performed duringconstruction by installing the diagonal struts on the portions of thetruss structure that are periodically shifted in the forward axialdirection off fixture 146.

While a preferred truss structure illustrated and described herein mayhave plane or puckered ends which include end struts joined to each ofthe two free vertex points, the invention is not so limited. It will beclear that the end struts at a plane or puckered end may be dispensedwith and a payload which connects the free vertex points structurallymay be substituted. In either case, the requisite structural integrityand stability are established.

Although frame feed units which utilize free wheeling belt units arepreferred, forced driving means for the belts may become necessary. Thisis particularly the case where the individual stack sizes areanticipated to be large. Under those conditions, forced belt drivingwill facilitate the frame element feeding process.

The preferred embodiment of the truss structure disclosed herein employssubstantially straight fixture pins with which to hold elements on theconstruction fixture. However, other types of pins may be used. Forexample, L-shaped pins with one leg perpendicular and the other parallelto a fixture plane could be employed. With such an arrangement, uponextension and rotation of the pin, it is the parallel leg which liesacross a portion of the frame element which serves to hold the latter.

Another type of fixture pin which may be used is an expandible pin ofthe type commercially available as Expando Pin from Adjustable BushingCorporation. The diameter of such a pin may be expanded or retracted bymechanical operation. Thus, if a substantially straight expandible pinis employed as a fixture pin, its diameter could be expanded afterinsertion into the mating fixture pin hole at the frame element vertex.This will result in a firm hold on the frame element. With such anarrangement, the diameter of the fixture pin must be reduced prior topin withdrawal.

The construction methods and construction apparatus are disclosed hereinin the construction of a truss structure in a gravity-free environment.However, the invention is not so limited and it will be understood thatthe aforesaid construction methods and apparatus therefor may alsooperate in a gravity environment.

While the preferred embodiment illustrated and described hereincomprises specific materials, components, apparatus and methods, it willbe obvious that numerous modifications, changes, variations,substitutions and equivalents, in whole or in part, will now occur tothose skilled in the art without departing from the spirit and scopecontemplated by the invention. Accordingly, it is intended that theinvention herein be limited only by the scope of the appended claims.

What is claimed is:
 1. A method for constructing an elongate prism-formtruss structure having a square cross section from a plurality ofplanar, congruent, triangular frame elements, said structure beingdefined by four longitudinal edges parallel to a central longitudinalaxis, said longitudinal edges defining structure planes therebetween,each of said frame elements having A-, B- and C-sides located oppositeA-, B- and C-vertices, the dimensions of said sides of said elementsbeing defined by:

    COS α=NC/4B

where α=included angle between said B- and C-sides at said A-vertex,α>90°, B=length of B-side, C=length of C-side, and N=integer>1; saidelements being fed from four feed points radially spaced from said axis;said method comprising the steps of:(1) feeding said elements in apredetermined sequence from said fed points such that each element isplaced into the confronting structure plane disposed between said feedpoint and said axis; (2) joining each element to selected ones of thepreviously fed elements such that said C-sides align along saidlongitudinal edges; and (3) repeating steps (1) and (2) until astructure of the desired length has been constructed.
 2. The method ofclaim 1 and further including the step of installing a plurality ofdiagonal struts extending between diagonally opposite longitudinalstructure edges, said struts intersecting said axis at points spacedalong the latter.
 3. The method of claim 1, wherein said elements arefed to a construction fixture from first, second, third and fourthstacks of said elements each located at one of said feed points, saidfirst and second stacks and said third and fourth stacks respectivelyfacing each other on opposite sides of said axis, said third and fourthstacks being displaced at a 90° angle around said axis with respect tosaid first and second stacks;said fixture conforming substantially tothe interior space of said structure under construction and beingcapable of axial movement relative thereto, said fixture includinglongitudinal edges parallel to and proximate the longitudinal edges ofsaid structure under construction and defining fixture planestherebetween each confronting one of said stacks; and said feeding stepfurther including placing the frame element currently being fed into aconstruction position on said fixture such that said element is disposedin said confronting fixture plane with its C-side lying adjacent one ofsaid longitudinal fixture edges.
 4. The method of claim 3 wherein N isan even integer no greater than 4;said first, second, third and fourthstacks mounted on first, second, third and fourth frame feed unitsrespectively, each of said feed units comprising a base plate andsubstantially identical telescoping guide posts mounted perpendicularlythereon each adapted to selectively extend in length, said guide postsbeing positioned on said plate in a pattern conforming to said frameelements and being capable of holding a predetermined number of saidframe elements in stacked relationship; said fixture including means forholding a plurality of frame elements thereon; each frame feedingoperation from a selected stack further comprising the steps of:selecting the top frame element of said stack with the free ends of thecorresponding guide posts; and extending said last-recited guide poststo place said selected element into its confronting constructionposition; said predetermined feed sequence comprising the steps of:feeding a first element from said third stack; feeding a second elementfrom said fourth stack; engaging said first and second elements withsaid fixture holding means while said guide posts remain extended inorder to retain said elements on said fixture; withdrawing said guideposts from said first and second elements respectively; moving saidfixture in a forward axial direction by a distance T with respect tosaid feed units, where T is substantially equal in length to the C-sideof an element; feeding the top element from each of said first, second,third and fourth stacks in sequence; joining each of the four last-fedelements to a previously fed element; holding the four last-fed elementsin construction position by maintaining the corresponding guide posts intheir extended position; disengaging said fixture holding means fromsaid first and second elements; moving said fixture in a backward axialdirection by said distance T; engaging said four last-fed elements withsaid fixture holding means; withdrawing said guide posts from said fourlast-fed elements; moving said fixture in said forward axial directionby said distance T; and repeating the above-recited steps commencingwith the feeding of the top frame element from said first stack.
 5. Themethod of claim 4 wherein each of said feed units is adapted to move inan axial direction;each of said frame elements including A-, B- andC-vertex fittings at the correspondingly designated vertices, saidA-vertex fitting including a substantially cylindrical socket alignedwith said C-side; said B-vertex fitting including a fastening pin havingan exposed portion extending outwardly therefrom and having an axisaligned with said C-side; said C-vertex fitting including a tabextending outwardly therefrom, said tab including a through-hole havingan axis substantially parallel to said C-side; said method furthercomprising the steps of: prior to feeding a given element from itsstack, moving the corresponding feed unit in a backward axial directionwith respect to said fixture by a distance F, where F exceeds the lengthof the exposed portion of said B-vertex fastening pin; upon extendingsaid guide posts with the currently fed element thereon, moving saidcorresponding feed unit in a forward axial direction by said distance F,said forward axial movement being effective to insert the B-vertexfastening pin of said currently fed element into the C-vertexthrough-hole of the previously fed element positioned on the adjacentface of said fixture nearest the C-side of said currently fed element,and thereafter to insert said pin into the A-vertex socket of theelement previously fed from the same stack.
 6. The method of claim 4 andfurther including the step of feeding an element from said first stackprior to feeding said first element from said third stack.
 7. The methodof claim 4 and further including the step of feeding an element fromsaid second stack prior to feeding said first element from said thirdstack.
 8. The method of claim 7 wherein:N=2, C=2B/√3,and wherein each ofthe opposite terminating ends of said structure includes first andsecond free vertices; said method further including the steps of:interconnecting said first and second free vertices with a first endstrut; and interconnecting said second free vertex to said structurewith a second end strut.
 9. The method of claim 4 and further including,prior to feeding said first element from said third stack, the stepsof:feeding an element from said first stack; and feeding an element fromsaid second stack.
 10. The method of claim 9 wherein:N=2, C=2B/√3,andwherein each of the opposite terminating ends of said structureincluding first and second free vertices; said method further includingthe steps of interconnecting said first free vertex with a junction of apair of element vertices on said structure by means of a first endstrut; and interconnecting said second free vertex with an additionaljunction of a pair of element vertices on said structure by means of asecond end strut.